In placing drainage node to the carriageway or kerb/curb lines in 2D plan, it is useful to show the flow arrow from high point to low point for the drainage engineer.
Currently, the flow arrow is only available in "Terrain", but not civil geometry or 3D linear linework.
@Guest this can be done using existing functionality, as described here: OpenRoads | OpenSite Forum - ORD R4U6: How do I show flow arrows in the plan view on our roadway ditches? - Communities (service-now.com). You will see though that this workflow adds the flow arrows to the 3D model, so you then need to turn on the display of the relevant level in the referenced 3D model to see the flow arrow in the 2D model. It might be possible to implement a more simple workflow in the future.